PPMXL Catalog Column Descriptions

PPMXL Overview

PPMXL is a catalog of positions, proper motions, 2MASS- and optical photometry of 900 million stars and galaxies, aiming to be complete down to about V=20 full-sky. It is the result of a re-reduction of USNO-B1 together with 2MASS to the ICRS as represented by PPMX.

For more details, see Roeser, Demleitner, & Schilbach (2010). Background for the USNO-B catalog is given here, while 2MASS documentation is available here.

PPMXL Catalog Column Descriptions

Gator serves the PPMXL Catalog (25 columns, 910,468,710 data rows). The column descriptions can be found below.

Name Intype Units Description
ipix int8 Identifier (Q3C ipix of the USNO-B 1.0 object)
ra double deg Right Ascension J2000
dec double deg Declination J2000
e_raepRA real deg Mean error in RA*cos(delta) at mean epoch
e_deepDE real deg Mean error in Dec at mean epoch
pmRA double deg/yr Proper Motion in RA*cos(delta)
pmDE double deg/yr Proper Motion in Dec
e_pmRA real deg/yr Mean error in pmRA*cos(delta)
e_pmDE real deg/yr Mean error in pmRA*cos(delta)
nobs int Number of observations used. nobs may be NULL for stars coming from ARIHIP or Tycho-2 via PPMX (i.e. bit 1 is set in flags).
epRA real yr Mean Epoch (RA)
epDE real yr Mean Epoch (Dec)
Jmag double mag J selected default magnitude from 2MASS
e_Jmag real mag J total magnitude uncertainty
Hmag double mag H selected default magnitude from 2MASS
e_Hmag real mag H total magnitude uncertainty
Kmag double mag K_s selected default magnitude from 2MASS
e_Kmag real mag K_s total magnitude uncertainty
b1mag double mag B mag from USNO-B, first epoch (see Note 1)
b2mag double mag B mag from USNO-B, second epoch (see Note 1)
r1mag double mag R mag from USNO-B, first epoch (see Note 1)
r2mag double mag R mag from USNO-B, second epoch (see Note 1)
imag double mag I mag from USNO-B (see Note 1)
magSurveys int Surveys the USNO-B magnitudes are taken from. Digits assigned to the surveys for b1mag, b2mag, r1mag, r2mag, and imag are concatenated (in that order). Digits are those given in Note h to Table 3 in USNO-B except both 7 and 9 in Note h are 7 here.

From this field, you can also see which of the surveys contributing to USNO-B had positions for the object.
flags int
bitmeaning
0One of the coordinates had excessively large chisquare
1Row is from PPMX. These objects are mostly Tycho stars that were masked out of USNO-B. For these, the USNO magnitudes (b1mag through imag) have special meanings, see Note 1.
2Row is from PPMX and replaces a single row from USNO-B. This is done when the astrometry from PPMX was better than the astrometry of the corresponding PPMXL object.
3Row replaces multiple USNO-B objects. When PPMX contains an object that has more than one counterpart in PPMXL, all such counterparts are discarded on the assumption that they should have been matched in USNO-B or result from erroneous matches. For these rows, bit 1 is always 1.


Note 1

Magnitudes from USNO-B should be used with care. Photometric calibration may be severely off for some plates. For objects from PPMX (bit 1 set in flags), these magnitudes have a special meaning as per the following table:

PPMXL column PPMX column PPMX content
b1mag Cmag Catalogue magnitude from source
b2mag Bmag Johnson B magnitude
r1mag Rmag calc. Ru magnitude from source
r2mag N/A always None
imag Vmag Johnson V magnitude